1. Field of the Invention
The present invention relates to a method of extinguishing an electric arc which occurs in switchgears.
In particular, the invention relates to a method based on a new principle of extinguishing the electric arc in electric way instead of the previous physical way.
2. Description of the Background
Reliability and lifetime of an instrument with contacts depend on how to make the electric arc small and how to extinguish it fast. It is the vacuum technique mainly used in high voltage that is now most superior of the techniques for making an electric arc small and extinguishing it fast. In vacuum circuit breakers the contacts are working under vacuum. Under vacuum the electric arc arises weakly and is easily extinguished since there is little ionization medium there. But the vacuum arc extinguishers are not used in low voltage or high voltage of more than 30 kV since they are difficult to manufacture and their costs are expensive. They are now only used in the switchgears for 3 to 20 kV.
In the common low voltage contactors the methods of extinguishing the electric arc by contacting it to a metal grating or an asbestos board and cooling it are still used and are little changed. Recently studies for extinguishing an electric arc in the low voltage field are intensified and accordingly several treatises are being reported.
In the NingBo Center of Science and Technology in China a method of extinguishing the electric arc in a 380V/65 A contactor using a superconducting magnet was reported in 2008, and in Japan a current break-even method was reported that the electric arc is extinguished by charging a condenser with the supply voltage, then discharging it into a reactor and supplying reversely the resonance voltage to the contacts. But these methods are not yet commercialized due to expensive costs and difficulty of manufacturing.
The switchgears using a SCR or high-capacity transistor are also developed but they can not be used in high voltage or large current since the apparatuses using electronic components have weak dielectric strength and are easily destroyed by an electric shock.
Almost all the recent data are about the improvement of structure base on the existing principle and mainly about the methods of manufacturing circuit breakers by vacuum technique.
The objective of the present invention is to establish a method of extinguishing an electric arc occurring in a low or high voltage switchgear on the basis of a new principle which is completely different from the existing one.